The present invention relates to improved processes for spinning polybenzoxazole ("PBO") or polybenzothiazole ("PBT") fibers.
Lyotropic liquid-crystalline PBO and PBT are not thermoplastic. They are typically made into fibers by dry-jet, wet-spinning techniques, in which a dope that contains PBO or PBT polymer and an acid solvent is extruded through a spinneret, drawn across an air gap, and coagulated by contact with a fluid that dilutes the solvent and is a non-solvent for the polymer. The individual filaments formed by this process can be combined to form one or more fibers of varying size.
It is desirable to spin a large number of filaments for a long period of time at a high rate of speed. It is also desirable to produce a fiber containing many continuous filaments of a given cross-sectional area rather than producing a fiber containing fewer filaments of substantially larger individual cross-sectional area. However, thinner filaments are much more difficult to produce continuously because they have a greater tendency to break during spinning. It is desirable to provide a method which minimizes the number of filament breaks.